Apparatus for vacuum-evaporation of metals under the action of an electric arc

ABSTRACT

A method for vacuum-evaporation of metals under the action of an electric arc and using a magnetic field is characterized by the fact that for retaining a cathode spot of an electric arc, a constant magnetic field is substituted by a pulsed magnetic field whose intensity reaches a maximum when the cathode spot is shifted to a non-evaporable cathode surface. This enables the travel of the cathode spot of electric arc to be unaffected by the inhomogeneity of the magnetic field and by any possible lack of perpendicularity of its lines of force to the surface being evaporated. A device for carrying out the method employs a sensor to take up the effect of electric arc, which is so arranged as to straddle the non-evaporable cathode surface and takes up the effect of electric arc only when the cathode spot is found on the non-evaporable cathode surface; the device is simple in design, smaller in size, and features a simplified-construction of an electromagnet that needs less power to be operated as compared to the prior-art devices used for vacuum-evaporation of metals under the effect of an electric arc.

MTRM- United States Patent 1191 Sablev et al. Jan. 1, 1974 APPARATUS FOR3,555,347 1/1971 Dickinson 219/121 EB x 3,576,438 4/1971 Pease 219/121EB x VACUUM-EVAPORATION OF METALS UNDER THE ACTION OF AN ELECTRIC ARCFiled: Mar. 22, 1972 Appl. No.: 237,083

US. Cl. 219/123, 219/121 EB Int. Cl B23k 9/08 Field of Search 219/123,12] EM,

References Cited UNITED STATES PATENTS 10/1893 Coffin 219/123 X PrimaryExaminer R. F. Staubly A1t0rneyl-lolman and Stern [57] ABSTRACT A methodfor vacuum-evaporation of metals under the action of an electric arc andusing a magnetic field is characterized by the fact that for retaining acathode spot of an electric are, a constant magnetic field issubstituted by a pulsed magnetic field whose intensity reaches a maximumwhen the cathode spot is shifted to a non-evaporable cathode surface.This enables the travel of the cathode spot of electric arc to beunaffected by the inhomogeneity of the magnetic field and by anypossible lack of perpendicularity of its lines of force to the surfacebeing evaporated. A device for carrying out the method employs a sensorto take up the effect of electric arc, which is so arranged as tostraddle the non-evaporable cathode surface and takes up the effect ofelectric are only when the cathode spot is found on the non-evaporablecathode surface; the device is simple in design, smaller in size, andfeatures a simplified-construction of an electromagnet that needs lesspower to be operated as compared to the prior-art devices used forvacuum-evaporation of metals under the effect of an electric are.

2 Claims, 4 Drawing Figures PATENTEUJAH 11914 3.783.231

SHEET 10F 3 FIG. 1

PATENTEDJM 11914 3,783,231

SHEET 2 0| 3 PATENTEUJAN 1 1974 3.783.231

snm 30F 3 EVlWIIW/Z 3 APPARATUS FOR VACUUM-EVAPORATION OF METALS UNDERTHE ACTION OF AN ELECTRIC ARC BACKGROUND OF THE INVENTION 1. Field ofthe Invention The present invention relates to methods of and devicesfor vacuum-evaporation of metals, and has particular reference tomethods of vacuum-evaporation of metals by means of an electric arc andto devices for carrying said methods into effect.

Vacuum-evaporation of metals, in particular, under the efi'ect of anelectric arc, is used for applying metallic coatings or films to metaland dielectrics, as well as in sorption pumps.

2. Description of Prior Art Widely known in the art is a method ofarcevaporation of metals under vacuum, wherein an electric arc is struckacross a cathode made of the metal to be evaporated and an anode toevaporate the cathode metal. To provide metal evaporation from therequired cathode surface (hereinafter referred to as evaporable cathodesurface), a cathode spot of the electric arc is retained on said surfacewith the help of a timeconstant magnetic field whose lines of force areperpendicular to the evaporable cathode surface and make up an acuteangle with that cathode surface whose evaporation is undesirable (thissurface will hereinafter be referred to as non-evaporable cathodesurface).

A tendency of the cathode spot to move in a magnetic field from anobtuse angle towards an acute angle made up by the cathode surface andthe direction of the lines of magnetic force is used to return thecathode spot onto the evaporable cathode surface in case of itsspontaneous shifting onto the non-evaporable cathode surface.

The afore-discussed method is employed in widely used devices whichincludes a vacuum chamber accommodating a coneor spherical-shapedcathode and an anode, both being made of the metal being evaporated andconnected to a D.C. voltage source; permanent magnets located outsidethe vacuum chamber establish a constant homogeneous magnetic field atthe cathode surface so as to retain the cathode spot on the evaporablecathode surface. An acute angle made up by the lines of magnetic forceand the non-evaporable cathode surface is provided due to the abovesaidshape of the cathode.

Upon creating a required degree of rarefaction within the vacuumchamber, an electric arc is struck across the cathode and the anode bymomentarily contacting the cathode by a movable electrode. The arc burnsin the vapours of the metal being evaporated while randomly moving overthe cathode surface.

When the cathode spot of the electric arc, while randomly wandering overthe cathode surface, gets onto its non-evaporable area, the magneticfield causes the cathode spot to return onto the evaporable cathodesurface.

A disadvantage inherent in said method of arcevaporation of metals undervacuum resides in the presence of a magnetic field while the cathodespot of the electric arc is found on the evaporable cathode surface.

In this case, strict and rigorous requirements are to be met by thehomogeneity of the magnetic field at the evaporable cathode surface andby the perpendicularity of the lines of magnetic force to said surface,since if the field is inhomogeneous the cathode spot is shifted towardsits higher-intensity area, and when the lines of magnetic force areout-of-perpendicularity with the evaporable cathode surface, the cathodespot travels from an obtuse angle towards an acute angle with the resultthat the metal of the cathode evaporates unevenly and thus loses it trueshape which disturbs the stability of arcing and leads to incompleteutilization of the material of the cathode.

Disadvantages inherent in the known prior-art device stem for theaforesaid phenomena in the method of arcevaporation of metals and residein sophisticated construction and large size of the magnets used toestablish a homogeneous magnetic field so that in high-capacity plantsthe size and power consumption of the magnet exceeds reasonable limits;consequently, such prior art plants have not found wide commercialapplication.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a method for vacuum-evaporation of metals under the effect of anelectric are, which method makes it possible to dispense with the use ofa constant magnetic field to retain the cathode spot on the evaporablecathode surface and to eliminate the effect of the magnetic fieldinhomogeneity on the travel of the cathode spot over the evaporablecathode surface.

The herein proposed method for vacuumevaporation of metals under theeffect of an electric arc enables a uniform cathode evaporation with itsshape remaining unaffected.

It is another object of the present invention to provide a device thatwould be simpler in design and be capable of carrying into effect themethod for vacuumevaporation of metals under the effect of an electricare, as well as would employ a smaller-sized electromagnet that needsless power to be operated.

Said objects are attained due to the fact that in a method forvacuum-evaporation of metals under the effect of an electric arc,wherein the metal per se to be evaporated serves as a cathode, and acathode spot is retained on preset evaporable cathode surface by meansof amagnetic field whose lines of force form an acute angle with thenon-evaporable cathode surface, according to the invention a pulsedmagnetic field is established whose intensity reaches a maximum when thecathode spot is found on the non-evaporable cathode surface.

It is most expedient that the magnetic field be established only whenthe cathode spot drifts and gets onto the non'evaporable cathodesurface.

In conformity with the method of the invention, in a device for carryinginto effect the method of evaporating metals as set forth hereinabove,which is essentially a vacuum chamber accommodating a cathode made ofthe metal to be evaporated and an anode between which an electric arc isstruck to evaporate metal from the evaporable cathode surface, and thecathode spot is retained on the evaporable cathode surface, by means ofan electromagnet that establishes a magnetic field whose lines of forcemake up an acute angle with the non-evaporable cathode surface,according to the invention provision is made for a sensor to sense andtake up the effect of the electric arc, said sensor being so arrangedwith respect to the cathode as to take up the effect of the electric areonly when the cathode spot drifts to and is found on the non-evaporablecathode surface.

This enables the size and power consumption rate of the electromagnetthat establishes the magnetic field, to be substantially reduced and itsconstruction to be simplified.

Specifically, the sensor adapted to sense and take up the effect of theelectric arc when the cathode spot is found on the non-evaporablecathode surface, comprises an electrode which is under the anodepotential and straddles the non-evaporable cathode surface.

It is expedient to make use of a turn of the electromagnet coilestablishing the magnetic field, as an electrode.

As a result of the herein-disclosed invention, there are provided amethod for an arc-evaporation of metals and a device for carrying saidmethod into effect, wherein the construction of electromagnet issubstantially simplified, at the same time ensuring a uniform cathodeevaporation, the stability of the electric are remaining unaffected.Such a simplified construction of the electromagnet is attained due tothe fact that the herein proposed method does not require homogeneity ofthe magnetic field effective on the evaporable cathode surface. In asmuch as the maximum magnetic field intensity that is enough to returnthe cathode spot onto the evaporable cathode surface is established onlyat the instant the cathode spot drifts and gets onto the non-evaporablecathode surface, the size of the electromagnet and amount of powerconsumed for creating the magnetic field are reduced by many times.

The herein-disclosed invention enables also the shape of the cathode tobe simplified which makes possible, with the commensurable size of thedevice, an increase the stock of the evaporable cathode metal. Theinvention also makes possible the use of a cathode with large-areaevaporable surface and provides vacuumevaporation devices of practicallyunlimited production capacity.

BRIEF DESCRIPTION OF THE DRAWING The present invention will hereinafterbe best understood by making reference to the accompanying drawings,wherein:

FIG. 1 illustrates a device for vacuum-evaporation of metals, madeaccording to the present invention with particular reference to devicesfor sorption evacuation of active gases;

FIG. 2 illustrates a device for vacuum-evaporation of metal, madeaccording to the present invention with particular reference to devicesfor obtaining fine films on metal and dielectric work-pieces;

FIG. 3 illustrates a modified device for evaporation of metals withparticular reference to obtaining uniform metallic films on flat-shapedwork-pieces; and

FIG. 4 shows an oscillogram of the current of an electromagnet thatestablishes a pulsed magnetic field in the device of FIG. 2.

DESCRIPTION OF PREFERRED INVENTIVE EMBODIMENTS A device for sorptionevacuation of active gases as shown in FIG. 1, is designed as follows. Apump housing 1 made of a non-magnetic material is connected to theflange of a space 2 to be evacuated by bolts 3 and is packed with arubber seal 4. The housing 1 itself serves as a anode accommodates acathode 7 made of the metal being to be evaporated; the cathode isplaced on a water-cooled copper bed 5 which is insulated from thehousing 1 by means of an insulator 6. The cathode 7 which is expedientlyshaped as a disk is tightly forced against the cooled bed 5 with studs8. A cylindrical non-evaporable surface 9 of the cathode 7 is embracedwith an electrode 10 which is in fact a sensor adapted to sense and pickup the effect of an electric arc when the cathode spot is found on thenon-evaporable surface 9 of the cathode 7; the electrode 10 is fixed tothe cooled bed 5 through insulators (not shown) and has a recess 11 fora movable electrode 12 to strike an electric arc. The movable electrode12 is held through an insulator 13 to an armature 14 located inside atube 15 which is made of a non-magnetic material. A coil 16 of theelectromagnet is adapted to break the gap cathode movable electrode bycompressing a spring 17. Located outside the housing 1 is anelectromagnet 18 capable of establishing a magnetic field whose lines offorce pass at an acute angle to the non-evaporable surface 9 of thecathode 7. For pre-evacuation of the space 2 being vacuumized and of achamber 19 of a pump, as well as for evacuating inert gases that are notsorbable provision is made for a fore-pumping system, incorporating amechanical pump and a high-vacuum evacuation system which comprises avapour-oil diffusion pump (not shown) connected to a flange 20. Thecathode 7 made of an evaporable metal, viz. titanium, is connectedthrough a wire conductor 21 to one of the ends of the coil of theelectromagnet 16, while the other end of the electromagnet 16 isconnected via a wire conductor 22 to the negative pole of a power source23. The positive pole of the power source 23 is connected to the pumphousing 1 via a wire conductor 24. The electrode 10 is electricallyconnected to the housing 1 via a wire conductor 25 passing through thevacuum-tight insulator 6 and a resistor 26. The movable electrode 12 isconnected to the pump housing I through a resistor 30 and by means of aflexible conductor 27 and a wire conductor 28 passing through avacuum-tight insulator 29. The coil of the electromagnet 18 is connectedvia wire conductors 31 and 32 to the output of an amplifier 33 at whoseinput is delivered a signal taken from the resistor 26 via wireconductors 34 and 35.

The high-vacuum electric-arc sorption pump illustrated in FIG. I,operates as follows. Upon pumping out gas from the space 2 beingevacuated and from the chamber 19 by means of the fore-pumping systemtill a pressure of 1.10 to 5.10 mm Hg is reached, the movable electrode12 is used to strike an electric arc on the non-evaporable surface 9 ofthe cathode 7 at a cathode spot. The arc burns across the surface 9 ofthe cathode 7 and the electrode 10 which are connected via the resistor26 to the housing 1, i.e., the anode. A voltage drop effective acrossthe resistor 26 is impressed upon the input of the amplifier 33 to whoseoutput is connected the electromagnet 18. As a result, a current flowsalong the coil of the electromagnet R8 to establish a magnetic fieldwhich expels the cathode spot of the electric arc onto an evaporablesurface 36 of the cathode 7. As soon as the cathode spot travels fromthe surface 9 to the surface 36, current ceases flowing along theresistor 26 and the magnetic field created by the electromagnet 18,disappears. While randomly travelling over the evaporable surface 36 ofthe cathode 7 made of titanium, the cathode spot 37 causes metal toevaporate, whereupon the evaporated metal is deposited upon the innerwalls of the housing 1 (anode). Thus, titanium deposited upon the wallsof the housing 1 effects evacuation of active gases. In the course ofmetal evaporation process the cathode 7 grows hot; to cool down thecathode 7 a coolant is made to flow liquid along a passageway 38 made inthe cooling bed 5. Upon reaching a pressure of 1.10 to 1.10 mm Hg insidethe space being evacuated, the fore-pumping system is disconnected andthe highvacuum evacuation system is engaged to evacuate an active gas(viz., argon) remaining in the space 2 to be evacuated.

While performing randomwise motion over the evaporable surface 36 of thecathode 7, the cathode spot 37 of the electric arc periodically driftsand gets onto the non-evaporable surface 9, thus closing the circuitcomprising the surface 9, the electrode 10, the wire conductor 25, theresistor 26 and the housing 1 thereby energizing the electromagnet 18via the amplifier 33; as a result, the electromagnet 18 establishes amagnetic field that expels the cathode spot onto the evaporable surface36.

Thus, the magnetic field is established only when the cathode spot isfound on the non-evaporable surface 9 of the cathode 7.

FIG. 2 illustrates a device for a vacuum-deposition of fine films.Therein, the cathode 7 made of the metal being evaporated, isdisk-shaped, while the work pieces 39 on which metal is to be depositedare located oppositely to the cathode on the surface of an imaginarysphere 40 tangential to the evaporable surface 36 of the cathode 7. Acover 41 is made of a non-magnetic material, whereas an electromagnet4?. establishing a magnetic field, is mounted on the cover 41 and iselectrically connected through a wire conductor 43 to the cover 41 andthrough a wire conductor 44, thence to a housing 45 which serves as ananode. In this device the cover 41 serves as a sensor to pick up theeffect of electric are when the cathode spot is found on thenonevaporable surface 9 of the cathode 7.

The cathode 7 is fixed to a cooled bed 46 by the studs 8. The cooled bedhas a passageway 47 for the coolant liquid to pass; the latter is let inand out through pipe connectors 48 and 49. The cooled bed 46 isvacuumtightly attached to the cover 41 made of a nonmagnetic material,by means of an insulator 50. The cover 41 is fixed on a housing 45 bybolts 51 and nuts 52 and is insulated therefrom with an insulatinggasket 53, the rubber seals 4, an insulating bush 54 and insulatingwashers fitted onto the bolt 51.

A movable electrode 56 is fixed on the armature 14 through the insulatorl3.

Gas-evacuation procedure occurs through the use of the systems offore-pumping and high-vacuum evacuation (not shown in FIG. 2).

The device operates as follows. Upon reaching the degree of operatingvacuum inside the space of the housing 45, lower than 1.10" mm Hg,preferably to 10 mm Hg, the power source 23 is switched on to energizean electric arc. As a result, current starts flowing along the circuitcomprising the wire conductor 22, the magnet coil 16, the wire conductor21, the cooling bed 46, the cathode 7, the movable electrode 56, thewire conductor 57, the resistor 58, the wire conductor 59, the housing45 (anode), and the wire conductor 24, thereby inducing current in themagnet coil 16 with the result that the armature 14 gets pulledthereinto. An electric arc is thus struck across the evaporable surface36 of the cathode 7 and the movable electrode 56.

A soon as the cathode spot 37 is shifted to the nonevaporable surface 9of the cathode 7, current starts flowing in the circuit comprising thecathode 7, the cover 41, the wire conductor 43, the electromagnet 42,the wire conductor 44, the housing 45, the wire conductor 24, the powersource 23, the wire conductor 22, the magnet coil 16, the wire conductor21, the cooled bed 46, and the cathode 7. Magnetic field created by theelectromagnet 42, expels the cathode spot 37 onto the evaporable surface36 of the cathode 7, and current flowing along the electromagnet circuitis considerably diminished. An oscillogram of the current flowing alongthe electromagnet is represented in FIG. 4.

The oscillogram of the current of the electromagnet 42 is taken with thediameter of the titanium cathode 7 equal to 50 mm and a meanarc-discharge current of A.

A modofication of the device for evaporation of metals, as depicted inFIG. 3, serves for making uniform coatings or films on flat-shaped workpieces 60. To this end, a cathode 61 of the metal being evaporated isshaped as a flat ring and is disposed on a cooled bed 62. Non-evaporablesurfaces 63 and 64 of the cathode 61 are embraced by electromagnets 65and 66.

Turns 67 and 68 of the coils of the electromagnets 65 and 66 have aclearance with the non-evaporable sur' faces 63 and 64 of the cathode61, whereas turns 69 and 70 are connected through wire conductors 71 and72 to the housing 45 and a cover 73. The entire cathode unit is mountedon the cover 73 of the housing 45. In the course of operation of thedevice the cathode spot of electric arc, while randomly travelling overan evaporable surface 74 of the cathode 61, periodically gets into thegap between the non-evaporable surface 63 or 64 and the turns 67 or 68,with the result that aredischarge current starts flowing along theelectromagnet 65 or 66, creating a magnetic field whose lines of forcemake up an acute angle with the non-evaporable surface 63 and 64, andthe cathode spot of electric are returns onto the evaporable surface 74of the cathode 61.

The rest of the operating features of this modification are similar tothose described above.

What we claim is:

1. A device for vacuum-evaporation of metals under the effect of anelectric arc, comprising a cathode having an evaporable and anon-evaporable surface, said cathode being made of a solid metal to beevaporated by the cathode spot of said electric are randomly moving overthe evaporable surface of said cathode; an anode; means for generatingsaid electric are between said cathode and said anode; an electromagnetdisposed so that at least one turn of said electromagnet facing thenon-evaporable surface of said cathode forms a gap with saidnon-evaporable surface at the side of said evaporable surface of saidcathode, the size of said gap being such that when said cathode spotshifts on to said non-evaporable surface said electric arc strikes atleast partially between said nonevaporable surface and said turn of saidelectromagnet, said electromagnet being connected to said anode so thatelectric current flows in the turn of said electromagnet when saidelectric arc strikes between said nonevaporable surface and said turn, amagnetic field being' induced as a result of the flow. of said electriccurrent, said magnetic field having lines of force which form an acuteangle with said non-evaporable surface and force said cathode spot toreturn to said evaporable surface of said cathode.

2. A device for vacuum-evaporation of metals under the effect of anelectric arc, comprising a cathode having an evaporable and anon-evaporable surface, said cathode being made of a solid metal to beevaporated by the cathode spot of said electric are randomly moving overthe evaporable surface of said cathode; an anode; means for generatingsaid electric arc between said cathode and said anode; an electrodearranged so of said cathode.

1. A device for vacuum-evaporation of metals under the effect of anelectric arc, comprising a cathode having an evaporable and anon-evaporable surface, said cathode being made of a solid metal to beevaporated by the cathode spot of said electric arc randomly moving overthe evaporable surface of said cathode; an anode; means for generatingsaid electric arc between said cathode and said anode; an electromagnetdisposed so that at least one turn of said electromagnet facing thenon-evaporable surface of said cathode forms a gap with saidnon-evaporable surface at the side of said evaporable surface of saidcathode, the size of said gap being such that when said cathode spotshifts onto said non-evaporable surface said electric arc strikes atleast partially between said non-evaporable surface and said turn ofsaid electromagnet, said electromagnet being connected to said anode sothat electric current flows in the turn of said electromagnet when saidelectric arc strikes between said nonevaporable surface and said turn, amagnetic field being induced as a result of the flow of said electriccurrent, said magnetic field having lines of force which form an acuteangle with said non-evaporable surface and force said cathode spot toreturn to said evaporable surface of said cathode.
 2. A device forvacuum-evaporation of metals under the effect of an electric arc,comprising a cathode having an evaporable and a non-evaporable surface,said cathode being made of a solid metal to be evaporated by the cathodespot of said electric arc randomly moving over the evaporable surface ofsaid cathode; an anode; means for generating said electric arc betweensaid cathode and said anode; an electrode arranged so that when saidcathode spot shifts onto the non-evaporable surface said electric arcstrikes at least partially between said non-evaporable surface and saidelectrode; an electromagnet connected to said electrode and said anodeso that at least a part of the current of said electric arc strikingbetween said nonevaporable surface and said electrode flows in saidelectromagnet which is disposed so that when said current flows thereinit induces a magnetic field which forces said cathode spot to return tosaid evaporable surface of said cathode.